The present invention relates to a circuit for compensating for instrumental errors of a flow meter.
In a flow meter, an instrumental error has to be compensated for by using a compensation coefficient or the like so that measurement of a flow rate of a fluid may give a true volume.
Supposing that an instrumental error is E, a displayed volume is Vi, a volume actually flown is Vq, and a compensation coefficient is (1+.alpha.), there holds an equation: ##EQU1## or EQU Vq=(1+.alpha.).multidot.Vi Eq. (2)
The instrumental error E, which is a function of the flow rate Q, cannot be reduced beyond a certain limit by a mechanical means but may be successfully reduced to a negligible value if use is made of an electronic means. The electronic means for such an application has heretofore been proposed in various forms.
One of the proposed electronic means is applied to a flow meter of the type wherein a pickup coil or the like senses rotations of a rotor which is rotated by a fluid flowing through the flow meter, the rotations being converted into electric pulses. The error reducing means is constructed to vary the pulse rate of detected pulses in order that an error curve may undergo a parallel shift within a certain range of flow rates Q to bring the errors closer to zero in an average sense. However, it is difficult for such a prior art implementation to approximate the errors to zero over the entire range of flow rates.
In light of this, there has been proposed a system in which a plurality of sections are defined within an operable range of a flow meter and a ROM or like memory stores error compensation amounts matched to the individual sections. The parallel shift of the error curve in this system occurs over a width which differs from one section to another. This system, however, suffers from the drawback that because a single compensation amount is assigned to each compensation section, the error reaches a critical value unless the range is fractionalized into a number of sections and, therefore, without a memory having a disproportionate capacity.